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Parcel Alignment Failed - Alignment caused a neighbor parcel number of parts to change

JasonBessert

We are working on a MAJOR alignment of parcels in a new sub into an existing fabric. In this case, we forced ourselves to use the choice of "Toggle Selection to Surrounding Parcels" since the brand new parcels in the subdivision are aligned to brand new control points which are askew from the existing fabric data. The existing parcels must align to the new parcels so we toggled, which always comes with complications. In this case, the complication is this error about "Alignment caused a neighbor parcel polygon number of parts to change".

This is not the first time we have seen this error, and we would like to know a workaround. As you can see from the screengrab there are 444 selected features surrounding the new subdivision that need to be aligned to the new parcels, and from the error message, there might be one or more "problematic features" that are preventing the alignment from going through. How can we detect this feature and how would we go about fixing it such that the alignment will run though?

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Accepted answers

AmirBar-Maor

Hello @JasonBessert

The Alignment process moves points which in turn modifies lines and polygons.

Sometimes, especially with data that has small segments, a point can move in a way that changes the number of parts a polygon has. Think of a 'bow tie' shape. This is data corruption and we've implemented this check to prevent it from happening.
The tool compares the number of parts each polygon has before and after the alignment process to make sure it hasn't changed.

We usually see this when the data contains very small line segments or points that are very close to each other. You can use the Parcel Layers 'Too Short' or the Geoprocessing tool Find Adjacent Parcel Points to detect those.

Another case can occur when a curve diverges to a straight line: sometimes moving the end point can cause the curve to go under the line (when zoomed in).

I agree we should improve on communicating where the problem is.

If your data is clean of those cases and you are still getting this error the workaround is to either try to use Align Parcels on subsets of the data, until you identify the problematic area, and/or use the Align Feature tool.

All comments

AmirBar-Maor

Hello @JasonBessert

The Alignment process moves points which in turn modifies lines and polygons.

Another case can occur when a curve diverges to a straight line: sometimes moving the end point can cause the curve to go under the line (when zoomed in).

I agree we should improve on communicating where the problem is.

JasonBessert

Thanks Amir, we applied the last workaround that you suggested from that message to get the map change finalized, working the alignment in portions of the data. Seems like the option of selecting surrounding parcels in the fabric always seems to come with complications and it's to the point where we have a workflow of pre-adjusting the fabric to allow the new parcels/subdivisions to fit more snugly with the newly introduced parcels, such that we always use the new parcels as the features subject to the alignment.

You did bring up an interesting case regarding arc segments converging on a straight line, those are the trickiest and our favorite tool, Align Parcels has trouble working those cases, since there is no tolerance too small to perform the alignment without pressing data together in a manner that is undesired. Hopefully there can be a way additional functionality can be applied to prevent 'over-alignment' of these features, but I'm getting off-topic on the matter of the original tenor of my message in this thread.

Regards,

NickN

In case it's helpful, for situations like above, we typically go in and do an alignment along the curve to the point of intersection then back out along the intersecting line. This does require special attention and visiting these individually, but I haven't found a better way to do it either.

Screenshot 2025-03-17 141706.png

JasonBessert

This is awesome, I'll have to give that one a try next time, I'm surprised we haven't tried that ourselves yet to keep the data from 'chewing itself up'.

NickN

for what it's worth, I've been messing around more with this and perhaps setting the Method in the Align Features panel to "Snap line ends to path" also solves this issue since it doesn't add new vertices, but instead snaps endpoints within the alignment buffer to the alignment path.

In my previous screenshot, using that method and only aligning along the arc doesn't squish the yellow parcel along the curve, it only snaps the southwest corner to the curve.

JasonBessert

Thanks, Nick. I always tend to use "Fit Shapes to Path" since it seems to have the most success at 'grappling' the data together where I need it to, but I will try the "Snap Line Ends to Path" option a little more in these tricky cases. Earlier attempts at the snap line ends didn't seem to produce the results I was expecting, so I typically use Fit Shapes to path more often than not.

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